1. Field of the Invention
The invention generally relates to lead brass material which has been subjected to at least one intermediate annealing treatment, the material being particularly useful for formation of drawn rods having improved machineability. The invention also provides a process for the thermal treatment of drawn lead brass rods, the process involving at least one rapid annealing treatment carried out at a temperature between 425.degree. C. and a temperature which is 10.degree. lower than the solidus point of the brass.
2. Description of the Prior Art
Machining of lead brass rods, particularly by screw-thread cutting, typically produces long shavings which "curl" or wind up, thereby giving rise to the well-known problem of "blocking" which necessitates frequent manual intervention by the operator to clear and clean the work piece and work tool. Lead brass rods are typically formed by a drawing process wherein one or more intermediate annealing treatments occur during the drawing operation. The conventional intermediate annealing treatments, which are carried out in static furnaces or in passage furnaces during drawing operations, distorts the machineability of the brass both with regard to the fineness of the shavings and with regard to life span of the machining tool. This degradation can be attributed to the coalesence of the lead, that is, the gathering of fine inclusions distributed in a substantially uniform manner in the form of globules. It is thus the intent in the art to produce lead brass rods which can be subjected to screw-thread cutting on automatic, high-speed lathes which operate without supervision. The machining of prior art lead brass material gives rise to long shavings which curl and produce the well-known "blocking" effect, thus resulting in the need for frequent manual intervention by the operator. The present invention particularly provides a process for the thermal treatment of drawn rods made of lead brass, this brass material on machining resulting in fine and short shavings which causes the material to be particularly suitable for automatic screw-thread cutting.